Today, I was admitted to hospital for suspected kidney failure. I called my best friend to let her know I couldn't make it to her birthday party tonight. She seemed to be infinitely more upset that I wouldn't be able to give her a birthday present. FML

I'm sorry OP, I went to the hospital after a car crash on my way to the 'supposedly' best friends house for her birthday, and I ended up getting yelled at by her. She thought I was 'being a rude little pussy' to lie, instead of telling her I didn't want to go.
Moral- she's not a friend. I hope you got something you can keep or can take back. She sounds absolutely rude.

Imagine when it's wedding time how many bridezilla moments she'll have. And I'm not even thinking of the havoc she'll wreak on her guests' wallets when they see the gift registry. Don't count on her properly thanking people, either.
As for you, OP, I sincerely hope the kidney failure is a false alarm. If not, have a good and speedy recovery. Forget about the friend. Seriously? Forget about her.